1. Field of the Invention
The present invention relates generally to an optical isolator, and more particularly, to a ferrule attachment type optical isolator constructed to have an optical isolator main body inserted and fastened in a concave groove of a holder and which enables the direct attachment of the holder to an end face of a ferrule.
2. Description of the Related Art
As publicly known, the optical isolator is an irreversible optical device that permits the passage of light in one direction but blocks the passage thereof in the opposite direction. The optical isolator is employed, for example, in an optical communication system using a semiconductor laser as a light source, to prevent the laser beam from returning toward the light source as a result of reflection. This type of optical isolator generally has a polarizer, a Faraday rotator element and an analyzer arranged in this order along the optical path, with a permanent magnet, adapted to apply a magnetic field along the optical path to the Faraday rotator element, provided outside the Faraday rotator element. The Faraday rotator element is used to rotate the polarizing surface of the incident light 45 degrees by the magnetic field of the permanent magnet, and the optic axes (polarization transmission axes) of the polarizer and the analyzer are oriented at 45 degrees to each other.
A configuration has been recently proposed that is intended to directly attach the optical isolator to the end face of the optical fiber ferrule in order to further reduce the distance between the light receiving and emitting devices for size reduction. The optical isolator to be attached is configured, for example, so that the polarizer, the Faraday rotator element and the analyzer are inserted and fastened in a cylindrical permanent magnet, or so that the polarizer, the Faraday rotator element and the analyzer are laminated in advance with an adhesive and inserted in a permanent magnet. In any case, the polarizer and the analyzer are of the same specification, and one of the polarizer and the analyzer is rotated relative to the other with the optical axis at the center so that the optic axes thereof are oriented at 45 degrees to each other.
In the case of the configuration having the polarizer, the Faraday rotator element and the analyzer (collectively referred to as optical elements) inserted in a cylindrical permanent magnet while maintaining an optically necessary effective area, the size cannot be readily reduced comparably to the outer diameter of the ferrule. The reason is that the more compact the size becomes, the more difficult it becomes to fasten the optical elements and that the bonding strength weakens due to the reduced bonding area of the optical elements. As for the configuration adapted to laminate the polarizer, the Faraday rotator element and the analyzer in advance with an adhesive, although the assembly work is relatively easy, on the other hand, this configuration is prone to problems such as possible damage in the case of the passage of a high-power light beam due to the mediation of an adhesive in the optical path. Therefore, this configuration is limited in applications (conditions of use). Moreover, both of these configurations require man-hours/parts to adjust the orientation of the optic axes, thus resulting in high cost.